A conventional bicycle having electronic shifting device as disclosed in U.S. Pat. No. 7,798,929 utilizes a signal cable to connect an input element to a front derailleur unit and a rear derailleur unit. It also utilizes a power cable to connect a power supply to the input element, the front derailleur unit and the rear derailleur unit. The conventional bicycle has a complicated wiring structure, and the cables may increase total weight of the bicycle.
Another conventional bicycle having electronic shifting device is disclosed in U.S. Pat. No. 7,760,078. An input element transmits control signals to a front derailleur unit and a rear derailleur unit wirelessly, and each of the front derailleur unit and the rear derailleur unit has a battery serving as a power supply. Although the electronic shifting device of such conventional bicycle is operated wirelessly and has no complicated wiring structure, several batteries are needed, and radio frequency interference tends to occur when several electronic shifting devices are used in the same environment.